Semiconductor device manufacturing includes a process of etching a substrate by using plasma. Processing techniques have become complicated more and more along with complexification of device structures and miniturization of patterns. Accordingly, in many cases, plural kinds of etching gases are used sequentially, for example, in the formation of recesses for burying interconnections and, accordingly, products comprising compounds may be formed on a substrate and such products may remain on the surface of the substrate.
For example, in an etching process of forming recesses for burying Cu interconnections in an SiOCH film comprising Si (silicon), O (oxygen), C (carbon) and H (hydrogen) noted as an interlayer dielectric film of a low dielectric constant instead of silicon oxide films, a film of a compound of Si and C such as an SiC (silicon carbide) film is used in some cases as an etch stop film (so-called, etch stopper) for protecting the surface of the Cu interconnections against an etching gas for the SiOCH film. In a case of etching the SiC film, for example, by plasma of a CF gas, an Si-containing CF polymer is deposited on the surface of the Cu interconnection layer by the etching. Since the deposits cause increase of contact resistance, they have to be removed.
On the other hand, in a case of forming Cu interconnections by means of dual damascene, sacrificial films are often used for forming via holes connecting upper and lower layers and trenches as interconnection grooves for each layer simultaneously and an organic film is used as one of such sacrificial films. In a certain type of dual damascene, the organic film as the sacrificial film is sometimes etched succeeding to etching of the SiC film. In this case, since it is necessary to prevent oxidation of Cu interconnections exposed on the surface of the substrate, it is necessary to avoid the use of an etching gas containing oxygen, and a plasma process is conducted by using, for example, ammonia gas as an etching gas for the SiC film. With the use of the ammonia gas, the CF polymer described above is also etched simultaneously with the etching of the organic film, and this is an efficient process in this regard. Further, also in a case of removing only the CF polymer formed during the etching of the SiC film, it is more efficient to conduct the removing process (plasma process) using ammonia gas succeeding to the etching of the SiC film, compared with a case, for example, of conducting cleaning in a cleaning station.
However, when a plasma process using a CF series gas (etching of the SiC film in this example) is conducted, CF series deposits are deposited in the processing vessel. Thus, when a plasma process using an ammonia gas is conducted successively, the CF series deposits are decomposed by the plasma to release fluorine into the processing atmosphere and, as a result, an ammonium silicofluoride is formed on the surface of the silicon-containing film of the substrate, for example, over the whole surface of the substrate. Since the compound is toxic to human bodies, when the substrate is delivered to a working environment outside of the processing apparatus in a state where the compound is deposited on the substrate, this inevitably results in a worry of giving undesired effects on operators' health. Further, the compound is hygroscopic and may possibly absorb water of a high dielectric constant to increase the dielectric constant of the wafer, as well as it may possibly oxidize barrier metals or interconnection materials. Therefore, the compound has to be removed from the surface of the substrate.
JP2005-191275A (paragraphs [0006] and [0008], and FIG. 2) discloses a technique of cleaning a wafer by using water or alcohol by utilizing the hygroscopicity (water solubility) of the compound. However, if water or the like used for cleaning intrudes into the SiOCH film, this causes increase of the dielectric constant. Further, if the interconnection metal is exposed, the surface of the interconnection metal is oxidized.
JP2005-85956A (paragraphs [0041] to [0045]) discloses a method of cleaning ammonium silicofluoride deposited onto the inside of a chamber by using nitrogen trifluoride gas and oxygen gas, but does not describe removal of the ammonium silicofluoride deposited on the substrate.